Considerable scientific and public attention has recently been directed to the problem of medical iatrogenesis, defined in a number of ways. In particular, the Institute of Medicine has recently described medical errors as a major threat to the quality of the American healthcare system. Despite efforts to improve reporting and affect system change, considerable further research is necessary. There are several reasons to believe that the quality of care for children is also affected adversely by medical errors, but currenfly available pediatric information is limited to ease reports and single institution surveys, or studies off medication errors. Improvements in healtheare delivery for children require further research that quantifies the incidence of iatrogenic illness and its descriptive epidemiology. To initiate investigation in this area, we propose a series of analyses utilizing the Healthcare Cost and Utilization Project (HCUP) of the Agency for Healtheare Research and Quality (AHRQ). The Specific Aims of this project are 1) To quantify the proportion of pediatric discharges with hospital-reported medical injuries and 2) To describe the association of selected patient characteristics with hospital-reported medical injuries. Using HCUP data from 1988, 1991, 1994, and 1997 we will deterinine the proportion of non-newborn pediatric discharges with ICD-9 codes identifying medical errors. We will then examine patient socio-demographic characteristics, measures of health status and co-morbidity, and measures of "exposure" to hospital care for their association with medical injuries. These analyses will be replicated in a subset of surgical patients using an alternative definition of "medical injury" more likely to be noted in the medical record because they represent sentinel events and also influence charges for billing. In this way, the robustness of the observed associations can be determined. These modest and descriptive analyses are intended to address significant gaps in our own understanding of iatrogenesis in children.